The present invention relates to heat exchangers, such as a regenerator, utilizing a translating solid matrix for transferring heat between high and low temperature fluids, such as hot exhaust gas and a cold air/fuel stream.
Heat exchangers for transferring heat between flowing fluid streams operate in many different ways. For example, some heat exchangers, such as recuperators, have no moving parts. The fluid streams flow in separate streams through a stationary matrix which transfers heat between the streams by conduction. These types of heat exchangers are relatively massive and, in the event that a change in the rate of heat transfer is desired, the response time is slow. Also, one of the fluid streams, e.g., a liquid, is typically conducted through small tubes which are secured together by weld joints which, by their very nature, are subject to leakage.
A conventional regenerator type of heat exchanger conducts a hot gas flow and a cold gas flow through different sections of a rotating porous core, which can be in the form of a disc, a hollow cylindrical drum, blocks of material, spheres, or any other geometrical form which is arranged so that the core material is disposed in and heated in the hot gas flow and then is moved into the cold gas flow for the purpose of heating the cold gas flow. Once cooled, the core material is reintroduced into the hot gas flow, completing the cycle. The core material may be moved by rotation, translation, flow (as in the case of small spheres or other finely divided materials) or other means. In the typical example depicted in FIG. 1, a portion of a core 12 is heated to a quasi-steady temperature profile by the hot (exhaust) flow, and then that heated core portion heats up the cold (pressurized intake) flow. The core is rotatably mounted in a fixed ducting (not shown) which possesses stationary seals engaging the rotating core along areas 14 shown as broken lines in FIG. 1, to isolate the hot and cold flows from one another. The core may comprise, for example, a steel mesh, metal foils, metal honeycomb structures, or a multitude of passages oriented parallel to the direction of fluid flow. Because the core rotates about an axis A while the flow ducting is stationary, the core rotational speed is a controlling parameter determining the amount (rate) of the heat transfer, and thus, by adjusting the rotational speed, the amount of heat transferred to the cold gas can be adjusted. It will be appreciated that in any other arrangement involving a movable heat transfer core, the same effect may be achieved by varying the parameter analogous to rotational speed (i.e., translation speed in the case of blocks, flow rate in the case of finely divided materials, etc.)
A regenerator is less massive than a recuperator of comparable effectiveness, and has a quicker response time for changing the rate of heat transfer. Also, regenerators do not rely on welds for preventing leakage and thus are not susceptible to weld leakage.
It will also be appreciated that regardless of the particular regenerator configuration being used, if the cold and hot gas streams are at different pressures, leakage tends to occur between the cold and hot sides across the seal areas 14. Such leakage could be a problem if the regenerator were used in a small energy generating system wherein the hot gas constitutes an exhaust gas, and the cold gas constitutes a high-pressure air/fuel stream in route to being combusted. In that case, fuel (hydrocarbons) from the high pressure air/fuel stream would tend to leak into the lower pressure exhaust gas stream. Since the exhaust gas is typically eventually vented to atmosphere, there would result a release of air-polluting hydrocarbons into the atmosphere.
A regenerator having a drum type of core may be preferred over a disc core, because a drum core can be made smaller, is less susceptible to warping, and is of lighter weight. However, the leakage problem also exists in regenerators having drum type cores, cone type cores, cores composed of spheres, blocks, etc., i.e., in any arrangement wherein the ducts separating and conducting the high and low pressure gases are stationary and the core material is in motion.
Therefore, it would be desirable to minimize the leakage (and resulting pollution) problem in regenerators, especially, but not limited to, regenerators having a drum or disc type core.